Resiliency is an important consideration in any power system, regardless of the application. The issues to which the power system must be resilient vary based on the application. For example, on an offshore drilling vessel, the power system should be made resilient to flooding, fires, or a fault within an electrical bus that carries power from generators to electrical devices throughout the vessel.
An electrical system on a vessel conventionally includes multiple generators in compartmentalized units that are separated against fire and flood. The compartmentalized units prevent damage from fire or flood to one unit from propagating to another compartmentalized unit. However, control systems for the power system are not located in the compartmentalized units. Further, the control system relies on information from each of the generators in each of the compartmentalized units to control the power system. For example, a control system can determine whether or not and when generators can couple to a main power distribution bus. Although the loss of a generator or a control system may not result in a loss of all generators or control systems, the generators and their control systems are unable to function independently and can suffer reduced performance or be further damaged due to incorrect decisions made by a control system.
A breaker couples a generator to a power bus and can break the connection between the power bus and the generator based on commands from a control system. Each breaker is linked by signal cables to other breakers, and the status of each breaker is included in the logic of the control section of the breakers. Consequently, damage to a breaker in one compartment creates erroneous behavior in a breaker in another compartment. Thus, the overall resiliency of the power system is reduced. Each breaker may include logic that controls the breaker either in the same cabinet or external to the cabinet.
FIG. 1 is a schematic representation of a conventional method for using breakers 112, 114, 116 within a power system 100, such as in offshore drilling vessels. The breakers 112, 114, 116 are coupled between a main electrical bus 102 and generators 122, 124, 126, respectively. Barriers 150 may be placed between the generators 122, 124, and 126 to isolate operation of the generators 122, 124, and 126 should a fire, flood, or other catastrophe occur. Communication links 113, 115 couple the breakers 112, 114, 116 to each other. The breakers 112, 114, 116 also share a control power cable 199 used to provide power to the breakers 112, 114, 116. The main bus 102 can be connected as a single conductor or broken into multiple segments by tie breaker master/slave sets 151, 152 and 153, 154. Communication links 156, 157 couple the tie breaker sets 151, 152 and 153, 154, respectively, to each other. The tie breaker master/slave sets 151, 152 and 153, 154 also share a control power cable 199 used to provide power to the tie breaker master/slave sets 151, 152 and 153, 154.
The generator breakers 112, 114, 116 communicate the status of the generators 122, 124, and 126 over the communication links 113 115, 131. Logic within each of the breakers 112, 114, 116 is dependent upon the behavior of each of the other breakers 112, 114, 116. For example, if the breaker 112 is instructed to perform synchronization with the main bus 102, then the breaker 112 must first indicate to the breaker 114 not to perform synchronization, or vice versa. If breaker 114 indicates it is performing a synchronization, no other breaker can perform a synchronization even if such indication is faulty. Therefore, if a communication link 131, 132, 133 between the management system 130 and the generator breakers 112, 114, 116 fails or if the any breaker 112, 114, 116 itself fails, then access to the other healthy breakers is interrupted.
Additional communications links may be provided between the management system 130 and the breakers 112, 114, 116, respectively. However, the additional communications links increase complexity of the system 100 and the number of connections that must be made between barriers 150. Decisions to open and/or close the breakers 112, 114, and 116 may be made by the management system 130 based on input from a bus sensing units 140, 143, 144 coupled to the main bus 102. Communication is required between bus sensing units 140, 143, 144 and the management system 130 and between generator breakers 112, 114, and 116. Communication is required between bus sensing units 140, 143 and the tie breakers 151, 152 and communication is required between bus sensing units 143, 144 and the tie breakers 153, 154. These communications links increase complexity of the system 100 and the number of connections that must be made between barriers 150. Successful operation of the tie breakers sets 151, 152 and 153, 154 require communications between the tie breaker master 151 and its slave 152 and between the tie breaker master 153 and its slave 154. These communications links increase complexity of the system 100 and the number of connections that must be made between barriers 150. Furthermore, an operator using a management system 130 can communicate only to the master breaker 151 or 153 of the tie breaker sets 151, 152 and 153, 154. Therefore, if a communication link 134, 135 between the management system 130 and the master breaker 151 or 153, respectively, fails or if the master breaker 112 itself fails, then access to the other breaker 152, 154 is interrupted.
Two issues arise from the network of interconnected breakers 110 that can affect the resiliency of the power system 100. First, the breaker 112, 113, 114, 151, 152, 153, 154 can close onto the bus 102 when the bus 102 is unsuitable for receiving additional power from the generator 122, 124, 126 such as when there is a fault on bus 102, such as a ground or a short circuit or a fault caused by the incorrect connection of a faulty generator. Second, the network of interconnected breakers 110 lacks autonomy of operation, because the breakers 112, 113, 114, 151, 152, 153, 154 are reliant on data from each other to control the supply of power to the bus 102.
One conventional solution to improving resiliency is the use of barriers 150. The consequences of a fire or flood are limited by use of barriers 150. However, the fire or flood in a specific compartment will disturb the signals that cross the barrier 150. This can cause erroneous data to be passed to the compartments protected by barrier 150. The consequences erroneous data can disable or otherwise compromise the operation of the equipment in a compartment that has not been damaged by a fire or flood.